The invention relates to a method for the cylinder-selective control of a multi-cylinder, self-ignition, four-stroke internal combustion engine with cylinder-selective fuel injection, in which method is based on the rotational crankshaft angle and the instantaneous rotational crankshaft speed, as well as a device for carrying out this method.
When compared to an internal combustion engine with spark ignition, e.g. an Otto engine, an internal combustion engine with self-ignition, e.g. a diesel engine, offers fewer options for influencing the combustion method. Thus, the mixture preparation options of an Otto engine are not applicable at all. The operating principle for the diesel engine only permits influencing the start of the injection and the amount of fuel that is injected. Unavoidable differences in the components result in undefined variations in the behavior of the individual cylinders, which can lead to shortcomings with respect to fuel consumption, emission of harmful substances, vibration behavior, synchronizing behavior, acoustics and service life.
All of the component differences here must be understood to be deviations of the diesel engine components from their theoretical ideal value. Said component differences result from unavoidable production tolerances, as well as can be caused during the operation of the internal combustion engine through abrasion, deformation, deposits etc.
The shortcomings caused by the component differences above all concern the differences in those components diesel engine, which play a part in the fuel feed or the combustion operation.
Particularly encumbered with problems are the injection nozzles, for example, which have to meet the requirement that all injection nozzles of a diesel engine must have the exact same hydraulic flow rate for the fuel. This requirement is difficult to realize, owing to the strong dependence of the hydraulic flow rate on the condition of the injection nozzle bore or the fuel temperature or the injection nozzle temperature. A reduction in the hydraulic fuel flow rate for an injection nozzle of a diesel engine during the combustion cycle here leads to a reduction of the mean pressure in the respective cylinder and thus also to irregularities in the crankshaft rotations. The mean pressure is a value that includes the course of the combustion chamber pressure during the combustion cycle of a cylinder, and which can serve as a measure for the energy converted in this cylinder.
The differences in the mean pressure for the individual cylinders lead to different effects in the various operational ranges of the diesel engine. As a result of irregularities in the crankshaft rotation, vehicle parts such as steering wheel, mirror, etc. are stimulated to vibrate during the idling. In the partial load range, this causes an increased emission of pollutants or an increase in the fuel consumption, while in the full load range, the diesel engine does not reach its maximum performance level. The increased stress on the individual cylinders leads to a decrease in the service life of the diesel engine.
It is the object of the invention to specify a method for the control of self-igniting, four-stroke internal combustion engines of the aforementioned type, which method minimizes the effects of differences in the components for the fuel feed and the combustion system to make possible further improvements in the engine characteristics, e.g., the fuel consumption.
This object is achieved in accordance in that the invention with different parameters are derived in dependence on the rotational speed from the course of the curve of the rotational crankshaft speed, which parameters are correlated as closely as possible with the respective mean pressure in the combustion chambers of the internal combustion engine, and from which cylinder-selective correction values for the cylinder-selective equalizing of the mean pressures are determined and used.
In a modification of the invention, correction values can be determined, following the equalizing of the mean pressures, which cause a defined unequalizing of the mean pressures in the combustion chambers of the internal combustion engine. Thus, a cylinder could be fired, for example, to a lesser or greater degree to suppress vibrations or resonances in the motor vehicle.
The equalizing or defined unequalizing of the mean pressures in the combustion chambers of the internal combustion engine is caused by the cylinder-selective change in the injection site and the amount of fuel injected into the combustion chambers of the internal combustion engine.
It is provided here that the cylinder-selective changes in the injection site and the amount of fuel injected into the combustion chambers of the internal combustion engine are made such that the sum of the cylinder-selective changes is equal to zero, thereby ensuring that the operating state desired by the driver or the power output of the internal combustion engine is not changed.
It is preferable if two types of parameters from the course of curve for the instantaneous rotational crankshaft speeds are used to equalize the cylinder-selective mean pressures: the mean rotational speed values formed above a maximum 720 degree rotational angle for the crankshaft, divided by the number of cylinders, or the rotational speed amplitudes.
For this, the rotational speed amplitudes for the course of curve of the instantaneous rotational speed of the crankshaft are determined by averaging several instantaneous rotational speeds for the same rotational angle of the crankshaft for the periodically repeating operating cycle of the internal combustion engine, which operating cycle for the most part includes respectively two crankshaft rotations.
One advantageous modification of the invention consists in the storage of curve courses for the instantaneous rotational speeds of the crankshaft and/or cylinder-selective correction values for comparison purposes. In this case, the values can be stored following the production of the internal combustion engine, following a repair, or following optional intervals.
The stored curve courses for the instantaneous rotational speeds of the crankshaft and/or the cylinder-selective correction values can be used for the early detection of combustion problems and/or compression problems in the internal combustion engine. The result of an early detection can be displayed in the motor vehicle, or can be called up during an inspection in a special repair shop.
A further advantageous modification of the invention consists in that the rotational angle of the crankshaft is detected with a measuring device with signal transmitter on the crankshaft and that the instantaneous rotational speeds of the crankshaft are determined from this with the aid of a processing unit.
In order to clearly associate the periodically repeating operating cycle of the diesel engine, comprising two crankshaft rotations, with the rotational crankshaft angle, the camshaft can be provided with a measuring device with signal transmitter, which permits the detection of the rotational camshaft angle, thereby providing information on whether a cylinder is in the 1.sup.st or 3.sup.rd, or in the 2.sup.nd or 4.sup.th power stroke.
In addition, the measuring devices for the crankshaft and the camshaft can be monitored as to their efficiency. For this, the ratio of the signals emitted by the individual signal transmitters for the two measuring devices must be constant.
One modification provides that a separate signal transmitter for the measuring device on the crankshaft and for the measuring device on the camshaft is used for marking a specified rotational angle for the respective shaft.
In addition, signals from signal transmitters on the crankshaft and the camshaft can be used to check the synchronization between crankshaft and camshaft.
Alternatively, the rotational angle for the crankshaft and the rotational speed of the crankshaft can also be determined from the rotational angle of the camshaft.
The cylinder-selective equalizing or the defined unequalizing of the mean pressure in this case make it possible to influence the emission of pollutants, the fuel consumption, the vibration behavior, the synchronizing behavior, the service life and/or the acoustics of the internal combustion engine.
The various parameters do not reflect the cylinder-selective mean pressure without distortion, but are changed more or less in the various rotational speed ranges by lateral influences that depend on the rotational speed. It can follow from this that one parameter is correlated with the cylinder-selective mean pressures more in the lower rotational speed range while the other parameter is correlated more in the upper rotational speed range for a diesel engine, which makes it necessary to use the parameters in a way that is specifically tied to the rotational speed. The use of varied parameters for varied rotational speed ranges of the diesel engine permits the equalizing or defined unequalizing of the mean pressure in dependence on the instantaneous rotational crankshaft speed in order to exert different influences. In the range of 300 -700 rotations per minute, for example, a vibration reduction can be carried out on the basis of rotational speed amplitudes, while in the range of 3000-6000 rotations per minute, the combustion engine can be controlled so as to minimize the exhaust gas emissions on the basis of averaged, instantaneous values for the rotational crankshaft speeds.
It is possible to carry out further error diagnoses on the basis of information on cylinder-selective correction values for varied rotational crankshaft speeds. Thus, a low correction value with low rotational crankshaft speeds and a high correction value with high rotational crankshaft speeds for a cylinder lead to the conclusion of a reduced hydraulic flow rate for the respective injection nozzle.
Finally, one advantageous modification provides for a separate, independent fuel feed system as device for carrying out the method for each cylinder of the internal combustion engine, which fuel feed system respectively comprises an injection pump, a line and an injection nozzle, the so-called PLD system. The crankshaft is also provided with a measuring device for detecting the rotational angle of the crankshaft, as well as an associated processing unit for determining the instantaneous rotational speed of the crankshaft. In order to detect the rotational angle of the camshaft, the camshaft is provided with a measuring device for determining the instantaneous rotational speed of the camshaft.
The method according to the invention is described and explained below using the example of a four-cylinder diesel engine and in connection with the drawings.